The present invention disclosure relates generally to manufacturing execution systems and, in particular, to methods, systems, and computer program products for implementing product randomization and analysis in a manufacturing environment using a process order variable.
In manufacturing environments, products are grouped in lots as they travel through a process line. For example, in a semiconductor manufacturing facility, carriers transport 300 mm wafers to each process equipment in the line. Each lot may be contained in a front-opening unified pod (FOUP), and wafers have a set slot position within the FOUP. It is not uncommon for events that occur during processing to cause variability in the yield of wafers located in certain slot positions. One example relates to a two-chamber tool. If the first chamber is bad, wafers in odd slots tend to be lower yield than wafers in even slots. Without using a randomization tool, the slot position remains the same from the beginning of the processing line to the end. Therefore, autocorrelation of the slot position to tool chambers makes it difficult, if not impossible, to distinguish between the many multi-chamber tools in the line for the purpose of detecting the faulty chamber.
One current randomization method is to use mappers to physically randomize, or shuffle, the wafers in a FOUP at given points in the line. In this way, the cause of a slot signal can be identified to be between two randomization steps (depending upon the frequency of randomization) in the process line. However, this method is not without drawbacks. For example, physical randomization techniques increase the overall process time (i.e., the time required to shuffle the wafers), as well as increase the costs of production (e.g., additional costs for purchasing, installing, and maintaining the mappers). In addition, using physical randomization is likely to render it difficult to distinguish between wafer handling events.
Another current randomization method is to logically randomize wafers by processing them in a random order at the process tool. Drawbacks to traditional logical randomization techniques include the inability to distinguish process effects by wafer position or location versus by process order, as well as the inability to use slot location in performing slot pattern analysis.
What is needed therefore in a way to provide product randomization and analysis that overcome the aforementioned deficiencies.